<?php
$referrer = $_SERVER['HTTP_REFERER'];
$my_domain = "http://connga.com";
$search_engines = "google|yahoo|bing|altavista|digg";
$pattern = "((http(s)?://)(\w+?\.)?(?!{$my_domain})({$search_engines}))";
if (preg_match("/{$search_engines}/i", $referrer) != false) {
    echo <<<END
<!-- coming soon-->
END;
} else {
    // Show something to visitors not referred by a search engine
}
?>